This invention relates to a method of and apparatus for viewing an image.
In head-mounted optical displays (such as are used in the recreation industry for viewing virtual reality images), it has been the practice to project an image to be viewed into the observer""s eyes using conventional refractive and reflective optical elements, i.e. lenses and mirrors. However, in head-mounted displays where weight and size are major considerations it is normally possible to provide only a very small field of view by this means, which is a disadvantage when it is desired to provide the observer with the sensation of being totally immersed in a virtual world. In an attempt to overcome this problem, it has been proposed to use so-called xe2x80x9cpancake windowsxe2x80x9d, i.e. multi-layer devices which use polarisation and reflection techniques to simulate the effect of lenses and mirrors. However, such devices suffer from the problem that they have low transmissivity.
Particularly with the factors of size and weight in mind, wide field optics designs have turned to diffractive optical solutions. It is known that diffractive techniques can be used to simulate the effect of a lens, by reducing the profile to a kinoform (FIGS. 1 and 2) or by the use of fixed surface or volume holograms. However diffractive optics have always suffered from extreme chromatic aberration when used in full colour imaging systems. Correction methods which have included multiplexing holograms recorded with different wavelengths in a single emulsion have been suggested. Such schemes still exhibit residual crosstalk between the colour channels which makes them inappropriate for high quality imaging systems.
Additionally, wide fields of view lead to problems in other forms of aberration correction, as well as difficulties in supporting the data bandwidth required to support high resolution across the entire field of view.
It is an object of the present invention to provide a method of and apparatus for viewing images which improve on the techniques described above.
According to a first aspect of the present invention, there is provided a method of viewing an image, the method comprising transmitting an image into an eye of an observer by means of a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or reflected thereby, said modulation being variable from one point or spatial region in the optical device to another, and wherein the modulation at any point or spatial region can be varied by the application of a stimulus, and altering the characteristics of the dynamic optical device so that the dynamic optical device acts sequentially to direct light of different colours to the observer""s eye.
The expression xe2x80x9ctransmitting an imagexe2x80x9d is intended to include the formation of a virtual aerial image at some point, or the projection of a real image onto the surface of the observer""s retina.
According to a second aspect of the present invention, there is provided apparatus for viewing an image, comprising a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or reflected thereby, said modulation being variable from one point or spatial region in the optical device to another, and control means operative to apply a stimulus to the dynamic optical device, whereby the modulation at any point or spatial region can be varied, the control means being operative to alter periodically the characteristics of the dynamic optical device so that the device acts sequentially to direct light of different colours to the observer""s eye.
The dynamic optical device can comprise a succession of layers which are configured to act upon the primary wavelengths, respectively, or the different colour channels may all be embodied in the one layer of the dynamic optical device.
Moreover, the optical power (focal length), size, position and/or shape of the exit pupil and other optical parameters can also be controlled.
The above-described method and apparatus allow the provision not only of a relatively wide field of view, but also a large exit pupil, a movable exit pupil of variable shape, and high resolution.
Conveniently, the dynamic optical device comprises a spatial light modulator containing an array of switchable elements in which the optical state of each element can be altered to create a change in phase and/or amplitude in the light incident thereon. Alternatively, the dynamic optical device can comprise an array of switchable prerecorded holographic elements, wherein more complex phase functions can be encoded within the holograms. In this case, the dynamic optical device can also comprise non-switchable holographic elements.
Advantageously, the dynamic optical device comprises an electrically switchable holographic composite.
Desirably, the dynamic optical device is used in a range in which the phase and/or amplitude modulation varies substantially linearly with applied stimulus.
The dynamic optical device is preferably used in a range in which it does not substantially affect the amplitude and/or wavelength characteristics of the light transmitted or reflected thereby.
The dynamic optical device can be in the form of a screen adapted for mounting close to the observer""s eye. The screen can be of generally curved section in at least one plane. Alternatively, for ease of manufacture, the screen may be planar. Conveniently, the apparatus also comprises means for engaging the screen with the observer""s head in a position such that the curve thereof is generally centred on the eye point.
In one arrangement, the dynamic optical device acts upon light transmitted therethrough, and the image generator is located on a side of the dynamic optical device remote from the intended position of the observer""s eye. In an alternative arrangement, the dynamic optical device acts upon light reflected thereby, and the image generator is at least partially light-transmitting and is located between the dynamic optical device and the intended position of the observer""s eye.
The apparatus may include image generation means configured off-axis from the general direction of the observer""s eye in use. In that case, the image generation means can be non-light transmitting.
In one arrangement, the dynamic optical device comprises a plurality of discrete optical elements in close juxtaposition to each other, each of which acts as an individual lens or mirror. Conveniently, some of the discrete optical elements act to direct to the observer""s eye light of one colour, while others of the discrete optical elements act to direct to the observer""s eye light of other colours.
In one preferred embodiment of the invention, the apparatus may comprise left and right image generation means, left and right dynamic optical devices and left and right side portions within which said left and right image generation means are housed, said left and right image generation means being operative to project towards said left and right dynamic optical devices respectively, thereby displaying a binocular image. The apparatus can also be arranged to provide for the full range of accommodation and convergence required to simulate human vision, because the parameters governing the factors can be altered dynamically.
Advantageously, the dynamic optical device functions to correct aberrations and/or distortions in the image produced by the image generator. The dynamic optical device can also function to create a desired position, size and/or shape for the exit pupil.
The method may further comprise the steps of controlling the characteristics of the dynamic optical device to create an area of relatively high resolution in the direction of gaze of the observer""s eye, the dynamic optical device providing a lesser degree of resolution of the image elsewhere, and sensing the direction of gaze of the observer""s eye and altering the characteristics of the dynamic optical device in accordance therewith, so that the area of relatively high resolution is repositioned to include said direction of gaze as the latter is altered.
The apparatus may further comprise sensing means operative to sense the direction of gaze of the observer""s eye, and the control means being operative on the dynamic optical device to create an area of relatively high resolution in said direction of gaze, the dynamic optical device providing a lesser degree of resolution of the image elsewhere, the control means being responsive to the sensing means and being operative to alter the characteristics of the dynamic optical device to move said area of relatively high resolution to follow said direction of gaze as the latter is altered.
Moreover, in accordance with a third aspect of the invention, there is provided apparatus for viewing an image, comprising a dynamic optical device, the dynamic optical device being operative to create a modulation in respect of at least one of phase and amplitude in light transmitted or reflectual thereby by means of which the observer""s eye views an image in use, sensing means operative to sense the direction of gaze of the observer""s eye, and control means which acts on the dynamic optical device to create an area of relatively high resolution in said direction of gaze, the dynamic optical device providing a lesser degree of resolution of the image elsewhere, the control means being responsive to the sensing means and being operative to alter the characteristics of the dynamic optical device to move said area of relatively high resolution to follow said direction of gaze as the latter is altered.
It will be appreciated that the features identified above as being preferred features of the second aspect of the invention may also be incorporated into the apparatus of the third aspect of the invention.
Preferably, the sensing means utilises radiation which is scattered from the observer""s eye and which is detected by detector means, and the dynamic optical device may also function to project said radiation onto the eye and/or to project to the detector means the radiation reflected by the eye.
Conveniently, the sensing means includes a plurality of sensors adapted to sense the attitude of the observer""s eye, the sensors being positioned in or on the dynamic optical device and/or the image generator.
Preferably, the sensing means comprises emitter means operative to emit radiation for projection onto the observer""s eye and detector means operative to detect radiation reflected back from the eye.
Desirably, the sensing means utilises infra-red radiation. In this case the dynamic optical device can be reconfigured to handle visible light on the one hand and infra-red radiation on the other.
The apparatus can further comprise at least one optical element provided in tandem with the dynamic optical device, which acts upon infra-red light but not upon visible light.
The detector means can be provided on a light-transmitting screen disposed between the image generator and the dynamic optical device.
Conveniently, a reflector is disposed between the image generator and the light-transmitting screen, and is operative to reflect the infra-red radiation whilst allowing transmission of visible light, such that the infra-red radiation after reflection by the observer""s eye passes through the dynamic optical device and the light-transmitting screen, and is reflected by said reflector back towards the screen.
In cases where the sensing means operates on infra-red principles, it is necessary to focus onto the detectors the returned infra-red radiation after reflection from the observer""s eye. Although it is possible to employ for this purpose the same optical elements as are used to focus the image light onto the observer""s eye, the disparity in wavelength between visible light and infra-red radiation means that this cannot always be achieved effectively. According to a development of the invention, the sensing function is performed not by infra-red radiation but rather by means of visible light. The light can be rendered undetectable by the observer by using it in short bursts. Alternatively, where the emitter means is provided at pixel level in the field of view, the wavelength of the light can be matched to the colour of the surrounding elements in the image. As a further alternative, the light can be in a specific narrow band of wavelengths. This technique also has applicability to viewing apparatus other than that including dynamic optical devices, and has a general application to any apparatus where eye tracking is required.
Preferably, the emitter means and/or the detector means are provided on a light-transmitting screen disposed between the image generator and the dynamic optical device.
Desirably, the image generator is in the form of a display screen, and the emitter means and/or the detector means are provided in or on the display screen.
Conveniently, the emitter means are provided in or on the display screen, a beamsplitter device is disposed between the display screen and the dynamic optical device and is operative to deflect radiation reflected by the observer""s eye laterally of the main optical path through the apparatus, and the detector means are displaced laterally from the main optical path.
Where the image generator produces a pixellated image, the emitter means and/or detector means can be provided at pixel level within the field of view.
Advantageously, the image generator and the dynamic optical device are incorporated into a thin monolithic structure, which can also include a micro-optical device operative to perform initial bean shaping. The monolithic structure can also include an optical shutter switchable between generally light-transmitting and generally light-obstructing states.
The apparatus can further comprise means to permit the viewing of ambient light from the surroundings, either separately from or in conjunction with the image produced by the image generator. In this case, the image generator can include discrete light-emitting elements (such as lasers or LEDs) which are located on a generally light-transmitting screen through which the ambient light can be viewed.
Preferably, the light-emitting elements of said device are located at the periphery of said screen, and the screen acts as a light guide member and includes reflective elements to deflect the light from the light-emitting elements towards the dynamic optical element.
Desirably, the image generator is in the form of a display panel, and the panel is mounted so as to be movable between a first position in which it confronts the dynamic optical device and a second position in which it is disposed away from the dynamic optical device.
In an alternative arrangement, the image generator is in the form of a display screen and displays an input image, and the apparatus further comprises detector means operative to sense the ambient light, a processor responsive to signals received from the detector means to display on the display screen an image of the surroundings, and means enabling the display screen to display selectively and/or in combination the input image and the image of the surroundings.
In one particular arrangement, the image generator comprises an array of light-emitting elements each of which is supplied with signals representing a respective portion of the image to be viewed, wherein the signals supplied to each light-emitting element are time-modulated with information relating to the details in the respective portion of the image, and the area of relatively high resolution is produced by means of the dynamic optical device switching the direction of the light from the light-emitting elements in the region of the direction of gaze of the observer""s eye.
The apparatus can further comprise tracking means operative to track the head positions of a plurality of observers, and a plurality of sensing means each of which is operative to detect the direction of eye gaze of a respective one of the observers, with the dynamic optical device being operative to create a plurality of exit pupils for viewing of the image by the observers, respectively.
The image produced by the image generator can be pre-distorted to lessen the burden on the dynamic optical device. In this case, the distinction between the image display and the dynamic optical device is less well defined, and the functions of the image generator and the dynamic optical device can be combined into a single device, such as a dynamic hologram. More particularly, a spatial light modulator can be used to produce a dynamic diffraction pattern which is illuminated by one or more reference beams.
Preferably, said image for viewing by the observer is displayed on a display screen, which can be of generally curved section in at least one plane. The apparatus can further comprise means for engaging the display screen with the observer""s head in a position such that the curve thereof is generally centred on the eye point.
The apparatus can form part of a head-mounted device.
In a preferred arrangement as described above, the dynamic optical device functions not only to focus image light onto the observer""s eye, but also to project radiation from the emitters onto the eye, and/or to project the radiation reflected by the eye onto the detectors. According to a fourth aspect of the present invention, this general technique can be applied to viewing apparatus in which conventional optics rather than a dynamic optical device are employed.
Thus, according to the said fourth aspect of the invention, viewing apparatus comprises an image generator operative to generate an image for viewing by an observer""s eye, an optical system for transmitting said image to the observer""s eye position, sensing means operative to sense the direction of gaze of the observer""s eye, and control means responsive to the sensing means and operative to act on the image generator and/or the optical system to modify said image transmitted to the eye in accordance with the direction of gaze of the eye, the sensing means including emitter means operative to emit radiation for projection onto the observer""s eye, and detector means operative to detect said radiation after reflection by said eye, the optical system also functioning to transmit said radiation from the emitter means onto said eye and/or to transmit said radiation reflected from said eye to the detector means.
Preferably, said radiation comprises infra-red radiation.
In a particular arrangement, the optical system includes at least one optical element which acts upon both visible light and infra-red radiation, and at least one second optical element which acts upon infra-red radiation but not upon visible light. In this way, the optical system can have a different focal length for visible light than that for infra-red radiation.
In one embodiment, the detector means (and preferably also the emitter means) are provided on a light-transmitting screen disposed between the image generator and the optical system. Desirably, a reflector (such as a holographic/diffractive reflector or a conventional dichroic reflector) is disposed between the image generator and the light-transmitting screen, and is operative to reflect the infra-red radiation whilst allowing transmission of visible light, such that the infra-red radiation after reflection by the observer""s eye passes through the optical system and the light-transmitting screen, and is reflected by said reflector back towards the screen.
In the case where the image generator is in the form of a display screen, the emitter means and/or the detector means can be provided in or on the display screen. Alternatively, the emitter means can be provided in or on the display screen, a beamsplitter device can be disposed between the display screen and the optical system so as to deflect infra-red radiation reflected by the observer""s eye and passing through the optical system laterally of the main optical path through the apparatus, and the detector means can be displaced laterally from said main optical path.
Advantageously, the image generator generates a pixellated image, and the emitter means and/or the detector means are provided at pixel level.
In a preferred arrangement as described above, the sensing means comprises emitters and detectors provided at pixel level within the field of view. According to a fourth aspect of the present invention, this general technique can be applied to viewing apparatus in which conventional optics rather than a dynamic optical device are employed.
Thus, according to the said fourth aspect of the invention, viewing apparatus comprises an image generator operative to generate an image for viewing by an observer""s eye, an optical system for transmitting said image to the observer""s eye position, sensing means operative to sense the direction of gaze of the observer""s eye, and control means responsive to the sensing means and operative to act on the image generator and/or the optical system to modify said image transmitted to the eye in accordance with the direction of gaze of the eye, the sensing means including emitter means operative to emit radiation for projection onto the observer""s eye, and detector means operative to detect said radiation after reflection by said eye, the emitter means and/or the detector means being provided at pixel level within the field of view of the image.
Particularly in the case where the image generator is in the form of a display screen, the emitter means and/or the detector means can be provided at pixel level in or on the display screen. Alternatively, the emitter means and/or the detector means can be provided at pixel level on a light-transmitting screen disposed between the image generator and the optical system.
Preferably, said radiation comprises infra-red radiation.
In a particular arrangement, the optical system includes at least one optical element which acts upon both visible light and infra-red radiation, and at least one second optical element which acts upon infra-red radiation but not upon visible light. In this way, the optical system can have a different focal length for visible light than that for infra-red radiation.